Type 2 diabetes and obesity trends in the Pacific Islands

Type 2 diabetes mellitus (T2DM) is a major risk factor for cardiovascular disease and contributes to premature mortality. T2DM has been reported to be a growing problem in the Pacific based on intermittently conducted population surveys over several decades. However, each survey has employed different selection and measurement criteria rendering the description of accurate trends impossible. Standardised STEPS (STEPwise approach to surveillance) surveys have been conducted by WHO. From two STEPS surveys conducted in each country, it has been reported that T2DM prevalences in Fiji, Samoa, and Tonga have doubled over a ten year period. These rapid increases are erroneous due to the incorrect application of the glucose cut-point in the later surveys. These findings have had significant impacts in affected countries and international agencies, and resulted in corrections of procedures. When all available population surveys were standardised to minimise selection and measurement bias, T2DM prevalence has increased in adults aged 25-64 years in Fiji (1980-2011), Samoa (1978-2013), and Tonga (1973-2012).T2DM incidence is more sensitive than prevalence in measuring the impact of preventive interventions, and is important in investigating aetiology as it is unaffected by survival. Current methods used to calculate T2DM incidence have drawbacks: cohort studies are expensive, are affected by differential attrition bias, and repeat testing can result in Hawthorne effects; registries do not capture undiagnosed individuals or diagnosed individuals who do not require medication; self-reported cases from repeat surveys exclude undiagnosed cases; and incidence calculated from compartment models require accurate cause-specific mortality data which are unavailable in low resource countries. A standard method of calculating tuberculosis incidence from sequential population Mantoux surveys has been adapted to determine T2DM incidence from recurrent population surveys of T2DM prevalence. T2DM incidence has increased in Fiji and Samoa over three decades. This novel method of calculating incidence utilises already existing prevalence surveys by applying integral calculus to birth cohort prevalences from an age-period matrix.Statistical approaches have been developed to include body mass index changes into projections of T2DM prevalence and incidence derived from recurrent prevalence surveys from the same population, which adds to previous estimations based only on period trends and age.The majority of the empirical work in this thesis has been published in four peer reviewed scientific journals with the PhD candidate as first author